Introduction The non-dipper hypertension (HT) pattern is associated with more end-organ damage and cardiovascular events than is dipper HT. Inflammation is widely established to play a role in the pathophysiology of HT. Recently, a new inflammatory and prognostic marker called the systemic immune-inflammation index (SII) has emerged. Our goal is to determine whether there is a relationship between non-dipper HT and SII. Methods Our study is a single-center retrospective and ninety-one patients with HT were included. All patients were analyzed with simultaneous 24-hour ambulatory blood pressure monitoring and laboratory parameters. Thirty-five patients had dipper HT while 56 patients had non-dipper HT. SII was calculated according to neutrophil, platelet, and lymphocyte counts. Results The median age was 48 (45-61 interquartile range (IQR)) in the non-dipper HT group, whereas it was 54 (44-64 IQR) in the dipper HT group. Although the neutrophil level, neutrophil-lymphocyte ratio, platelet lymphocyte ratio, SII, sleeping systolic blood pressure (BP), and sleeping diastolic BP were higher (p=0.020, p=0.041, p=0.046, p=0.019, p<0.001, and p=0.001, respectively) in the non-dipper HT group, the lymphocyte level was lower (p=0.040). A multivariate logistic regression model shows that SII (odds ratio (OR)=1.023, 95% confidence interval (CI)=1.002-1.112, p=0.012) may be an independent predictor of non-dipper HT. Conclusion Our study showed that the SII level was higher in the non-dipper HT patient group than in the dipper HT group. Furthermore, SII was an independent predictor of non-dipper HT. The high SII value in hypertension patients can be used as an early warning parameter to identify non-dipper HT patients.